biologically no, they can't be parents. but by that definition, you'd also have to tell every step parent on the planet that they are not a "parent."
Try to understand the point. Only a man and a woman can make a baby. From this is drawn the inference that God (or evolution) intended children to be raised by a man/woman union.
Thousands of years of human experience with this arranegment have proven the usefullness of this arrangement. Social science tells us of the advantage a child with mother and father has over those raised by a single parent.
Yet, you want to argue that it is somehow unfair to not chuck aside millennia of human experience, the logical inference from human biology, and Divine revelation because we suddenly know better than all of that.
SD